Intramultiplet mixing in collisions of calcium4s4pPJo3with helium: Measurement of state-to-state cross sections

An optical-pumping state-selection technique for the study of collisions of ${}_{}{}^3{}_{}{}^{}P$ atoms in individual spin-orbit states is described. This technique is used to determine state-to-state intramultipletmixing cross sections for collisions of $\mathrm{Ca}{}_{}{}^3{}_{}{}^{}P_{}^o{}_{}{}^{}$ with helium in a beam—static-gas arrangement. The derived cross sections are as follows: for $J=2\mathrm{}\to J^{\prime }=1, 31.9\pm 4.2$ ${\mathrm{\AA }}^2$; for $J=2\mathrm{}\to J^{\prime }=0, 5.5\pm 1.6$ ${\mathrm{\AA }}^2$; and for $J=1\mathrm{}\to J^{\prime }=0, 2.0\pm 5.0$ ${\mathrm{\AA }}^2$. These quantities represent averages over the translational-energy distribution (average energy 0.0556 eV). In the following paper Alexander, Orlikowski, and Straub present quantum close-coupling cross sections as a function of translational energy, using the pseudopotential Ca-He interaction curves of Malvern [J. Phys. B 11, 831 (1978)]. The experimental 2→1 and 2→0 cross sections are found to be 3 to 4 times larger than the calculated theoretical values. In contrast to the theoretical prediction for the ratio of the smaller cross sections, the 2→0 cross section is found to be larger than the 1→0 cross section.